Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $199.67   4.460%   $208.5753   $208.58   $208.60   $208.60  
  Purchase #2 $173.39   11.701%   $193.6784   $193.68   $193.70   $193.70  
  Purchase #3 $20.82   7.764%   $22.4365   $22.44   $22.45   $22.40  
  Purchase #4 $201.84   11.302%   $224.652   $224.65   $224.65   $224.70  
  Purchase #5 $129.65   11.206%   $144.1786   $144.18   $144.20   $144.20  
  Purchase #6 $156.62   7.227%   $167.9389   $167.94   $167.95   $167.90  
  Purchase #7 $162.70   12.385%   $182.8504   $182.85   $182.85   $182.90  
  7 purchase totals = $1,044.69       $1,144.3101   $1,144.32   $1,144.40   $1,144.40